circuit board

Abstract

To provide a circuit board which is improved in dielectric characteristics and long-term heat resistive connectivity and comprises a polyimide insulation layer.SOLUTION: A circuit board 1A comprises a wiring layer 10 and a polyimide insulation layer 100A in contact with the wiring layer 10. The circuit board comprises a thermoplastic polyimide layer 120A directly in contact with the wiring layer 10 and a non-thermoplastic polyimide layer 110 indirectly in contact with the wiring layer 10, and at least one or more of via connection parts are formed in the polyimide insulation layer 100A. The polyimide insulation layer 100A satisfies conditions that a heat expansion coefficient ranges from 10 to 30 ppm / K, an oxygen permeation degree is equal to or less than 1.8×10-12 mol / (m2 s Pa), a ratio of monomer residues having a biphenyl skeleton is 50 mol% or more with respect to all monomer residues induced from all monomer components constituting the non-thermoplastic polyimide layer and the thermoplastic polyimide layer, and an imide group concentration of the non-thermoplastic polyimide layer 110 is equal to or less than 33 wt.%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a circuit board having a polyimide insulating layer. [Background technology]

[0002] Polyimide resins are widely used in electronic devices, electrical devices, and electronic components as materials for circuit boards and other devices due to their high insulating properties, dimensional stability, easy moldability, and light weight. In particular, in recent years, the increasing performance and functionality of electronic devices and electrical devices has led to demands for faster information transmission, and the components and members used in these devices are also required to support high-speed transmission. Therefore, attempts have been made to reduce the dielectric constant and dielectric loss tangent of polyimide materials used in such applications so that they have electrical properties compatible with high-speed transmission.

[0003] Most of the conventional techniques for reducing the dielectric constant or dielectric dissipation factor of polyimide materials have mainly involved multilayering with resins with low dielectric constants or dielectric dissipation factors (such as fluororesins or liquid crystal polymers), compositing with different materials such as blending fillers with low dielectric constants or dielectric dissipation factors, making the polyimide porous, introducing ester structures, etc. However, combining and making the polyimide porous has problems such as a decrease in the processability of the polyimide material, and introducing ester structures has problems such as a decrease in the strength of the polyimide film, making it impossible to use large amounts of the ester structures.

[0004] Furthermore, Patent Documents 1 and 2 propose polyimide films that can be applied to high-frequency circuit boards by improving the dielectric properties through the use of innovative monomeric compositions for polyimides.

[0005] Meanwhile, in recent years, it has become necessary to assume that circuit boards will be used in environments exceeding 150°C. For example, flexible printed circuits (FPCs) used in automotive electronic devices may be repeatedly exposed to high-temperature environments of around 150°C. Flexible printed circuit boards are also increasingly being used in devices other than automotive electronic devices, such as laptop computers and supercomputers that have central processing units (CPUs) capable of high-speed processing, in order to further reduce their size and weight. In such devices, the heat generated by the CPUs repeatedly exposes flexible printed circuit boards to high-temperature environments.

[0006] A typical cause of deterioration of flexible printed circuit boards due to use in high-temperature environments is lifting or peeling of the wiring layer due to a decrease in adhesion between the wiring layer and the insulating resin layer.

[0007] Given this background, it is expected that flexible printed circuit boards will need to achieve both improved dielectric properties and the maintenance of heat-resistant adhesion in high-temperature environments (i.e., maintaining peel strength), and in particular, it is thought that maintaining heat-resistant adhesion over a long period of time will be required. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] WO2017 / 159274 [Patent Document 2] WO2018 / 061727 Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a circuit board having a polyimide insulating layer that is excellent in dielectric properties and long-term heat-resistant adhesion. [Means for solving the problem]

[0010] The present inventors have discovered that, in a circuit board having a polyimide insulating layer in contact with a wiring layer, the above-mentioned problems of the present invention can be solved by increasing the content ratio of monomer residues having a biphenyl skeleton in the polyimide constituting the polyimide insulating layer, and have completed the present invention.

[0011] That is, the circuit board of the present invention is a circuit board including a wiring layer, at least one polyimide insulating layer in contact with the wiring layer, and a plurality of via connections, At least one of the via connections is formed in the polyimide insulating layer, and the polyimide insulating layer has a thermoplastic polyimide layer that is in direct contact with the wiring layer and a non-thermoplastic polyimide layer that is in indirect contact with the wiring layer; The polyimide insulating layer meets the following conditions (i) to (iv): (i) The thermal expansion coefficient is in the range of 10 to 30 ppm / K; (ii) Oxygen permeability is 1.8 × 10 -12 mol / (m 2 ·s·Pa) or less; (iii) the proportion of monomer residues having a biphenyl skeleton, calculated by the following formula (1), relative to all monomer residues derived from all monomer components constituting the non-thermoplastic polyimide layer and the thermoplastic polyimide layer is 50 mol % or more: (iv) the imide group concentration of the non-thermoplastic polyimide layer is 33% by weight or less; The present invention is characterized in that:

[0012]

number

[0013] In the circuit board of the present invention, the polyimide insulating layer in contact with the wiring layer has a content of monomer residues having a biphenyl skeleton of 50 mol % or more, thereby suppressing oxygen permeability, providing excellent dielectric properties and long-term heat-resistant adhesion, and also providing good via processability. Therefore, the circuit board of the present invention is compatible with high-speed transmission, and the adhesion between the wiring layer and the polyimide insulating layer is maintained for a long period of time even in an environment where the circuit board is repeatedly exposed to high temperatures. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of a circuit board 1A of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a circuit board 1B of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view of a circuit board 1C of the present invention having a strip structure. [Figure 4] FIG. 4 is a schematic cross-sectional view of a circuit board 1D of the present invention having a microstrip structure. [Figure 5] FIG. 5 is a schematic cross-sectional view of a circuit board 1E of the present invention having a differential strip structure. [Figure 6] FIG. 6 is a schematic cross-sectional view of a circuit board 1F of the present invention having a coplanar structure. [Figure 7] FIG. 7 is a schematic cross-sectional view of a circuit board 1G of the present invention having yet another structure. [Figure 8] FIG. 8 is a plan view of a slit aluminum tape used in measuring oxygen permeability. [Figure 9] FIG. 9 is a cross-sectional view of a sample for measuring oxygen permeability of a polyimide film. [Figure 10] FIG. 10 is a cross-sectional photograph of a via hole formed in a circuit board taken by a scanning electron microscope (SEM). [Figure 11] FIG. 11 is a cross-sectional photograph of a through-hole formed in a circuit board taken by a scanning electron microscope (SEM). [Figure 12] FIG. 12 is a cross-sectional photograph taken with a scanning electron microscope (SEM) after plating via holes formed in a circuit board. [Figure 13] FIG. 13 is a scanning electron microscope (SEM) photograph of a cross section of a through-hole formed in a circuit board after plating. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or equivalent components.

[0016] <Overall structure> The circuit board of the present invention comprises a wiring layer, at least one polyimide insulating layer in contact with the wiring layer, and a plurality of via connections. At least one of the via connections is formed in the polyimide insulating layer. The polyimide insulating layer has a thermoplastic polyimide layer in direct contact with the wiring layer and a non-thermoplastic polyimide layer in indirect contact with the wiring layer. An insulating resin layer may be present to cover the wiring layer, and may be either a curable resin or a thermoplastic resin.

[0017] Here, the "thermoplastic polyimide layer" refers to a layer having a storage modulus of 1.0×10 at 30°C measured using a dynamic viscoelasticity measuring device (DMA). 9 Pa or more, and the storage modulus at 350°C is 1.0 × 10 8 A "non-thermoplastic polyimide layer" refers to a polyimide layer having a storage modulus of less than 1.0 x 10 Pa at 30°C measured using a dynamic viscoelasticity measuring device (DMA). 9Pa or more, and the storage modulus at 350°C is 1.0 × 10 8 By using a thermoplastic polyimide layer as the polyimide layer that is in direct contact with the wiring layer, the adhesion between the wiring layer and the polyimide layer can be improved.

[0018] Both the non-thermoplastic polyimide layer and the thermoplastic polyimide layer contain an acid dianhydride residue and a diamine residue as “monomer residues.” Here, the “acid dianhydride residue” refers to a tetravalent group derived from a tetracarboxylic dianhydride, and the “diamine residue” refers to a divalent group derived from a diamine compound.

[0019] 1 and 2 are schematic cross-sectional views of a main portion of a circuit board according to an embodiment of the present invention, each showing an example of the layer configuration of a polyimide insulating layer. Circuit board 1A shown in Fig. 1 includes wiring layer 10 and polyimide insulating layer 100A in contact with wiring layer 10. Polyimide insulating layer 100A includes thermoplastic polyimide layer 120A in direct contact with wiring layer 10 and non-thermoplastic polyimide layer 110 in indirect contact with wiring layer 10, more specifically, non-thermoplastic polyimide layer 110 in contact with thermoplastic polyimide layer 120A.

[0020] In addition, in the circuit board 1B shown in Figure 2, the polyimide insulating layer 100B in contact with the wiring layer 10 has a three-layer structure consisting of a thermoplastic polyimide layer 120A, a non-thermoplastic polyimide layer 110, and a thermoplastic polyimide layer 120B from the wiring layer 10 side. Although the via connection portions are not shown in FIGS. 1 and 2, at least one via connection portion is formed in the polyimide insulating layers 100A and 100B.

[0021] In the circuit board of the present invention, the layer configuration of the polyimide insulating layer in contact with the wiring layer is not limited to the examples shown in Figures 1 and 2, and for example, the total number of thermoplastic polyimide layers and non-thermoplastic polyimide layers may be four or more.

[0022] Furthermore, the arrangement of the wiring layer and polyimide insulating layer is not limited to the examples shown in Figures 1 and 2. Hereinafter, if the polyimide insulating layer, including the above-mentioned polyimide insulating layers 100A and 100B, is denoted by the reference numeral 100, for example, as shown in Figure 3, a strip-structured circuit board 1C may be formed in which wiring layers serving as ground layers 12 are provided on the front and back of a wiring layer serving as a signal line 11 via polyimide insulating layers 100. In Figure 3, reference numeral 20 denotes an adhesive layer. Note that although via connections are not shown in Figure 3, at least one via connection is formed in one or both of the two polyimide insulating layers 100 (the same applies to Figure 5).

[0023] As shown in Fig. 4, a circuit board 1D may have a microstrip structure in which a wiring layer serving as a ground layer 12 is provided on one side of a wiring layer serving as a signal line 11, with a polyimide insulating layer 100 interposed therebetween. A coverlay 30 consisting of an adhesive layer 20 and a polyimide film 130 may be provided on this signal line 11. Although via connections are not shown in Fig. 4, at least one via connection is formed in the polyimide insulating layer 100 (the same applies to Fig. 6). Also, as shown in FIG. 5, a differential circuit board 1E may be used in which signal lines 11 are provided in parallel on the same surface in a strip structure. As shown in FIG. 6, the circuit board 1F may have a coplanar structure in which the signal line 11 and the ground layer 12 are provided on the same plane.

[0024] 7, a circuit board 1G may be provided in which a signal line 11 and a shielding line 13 that electromagnetically shields the signal line 11 are provided on the same surface. In the circuit board 1G shown in FIG. 7, the signal line 11 and the shielding line 13 are formed on a first polyimide insulating layer 100′ that is laminated on a first ground layer 12′, and an adhesive layer 20 that covers the signal line 11 and the shielding line 13 is provided. A second polyimide insulating layer 100″ is laminated on the adhesive layer 20, and a second ground layer 12″ is further laminated on the second polyimide insulating layer 100″. Here, the terms “first” and “second” in the terms “first” and “second” for the first ground layer 12′ and the second ground layer 12″, and the first polyimide insulating layer 100′ and the second polyimide insulating layer 100″ are used for convenience of explanation, and they may have the same configuration or different configurations. The circuit board 1G shown in Figure 7 has multiple via connections 40 that penetrate from the first ground layer 12' to the second ground layer 12" in the stacking direction. The via connections 40 may be plated via holes (including through holes) or filled vias in which a conductor is filled inside the hole. The via connections 40 in Figure 7 are through holes that penetrate each of the first ground layer 12' / first polyimide insulating layer 100' / shield wiring 13 / adhesive layer 20 / second polyimide insulating layer 100" / second ground layer 12" in the thickness direction.

[0025] Here, typical methods for forming via holes (drilling methods) include drilling and laser processing using a UV-YAG laser, CO2 laser, or the like. In the circuit board 1G shown in FIG. 7, at least the first polyimide insulating layer 100' satisfies condition (iii). The proportion of monomer residues having a biphenyl skeleton is 50 mol% or more, resulting in excellent UV absorption. This allows for excellent processability when drilling vias with a UV-YAG laser. Furthermore, with CO2 lasers, the high biphenyl skeleton content facilitates carbonization, reducing damage around the carbonized layer and preventing deterioration of the via shape. Furthermore, the high biphenyl skeleton content enables both a low dielectric tangent and a high tensile modulus of elasticity. This reduces the step between adjacent layers during drilling, improving drilling processability. Furthermore, the high biphenyl skeleton content also improves strength, allowing for processing that minimizes breakage of the circuit board even when forming a large number of via holes, thereby improving the reliability and yield of the circuit board. In addition, in FIG. 7, the above effect can be obtained even when the second polyimide insulating layer 100'' has the same structure as the first polyimide insulating layer 100', and the via processability of the entire circuit board is further improved. The above-described effects of the polyimide insulating layer of the present invention are not limited to the structure shown in FIG. 7, but are also achieved in the same manner in circuit boards having the structures shown in FIGS. 1 to 6 and other structures.

[0026] <Wiring layer> The metal material constituting the wiring layer 10 is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or copper alloys are particularly preferred. When the wiring layer 10 is made of copper foil, rolled copper foil or electrolytic copper foil may be used. Commercially available copper foil can be used.

[0027] Furthermore, for example, for the purpose of rust prevention or improving adhesive strength, the wiring layer 10 may be subjected to a surface treatment using, for example, siding, aluminum alcoholate, aluminum chelate, a silane coupling agent, or the like.

[0028] Although the thickness of the wiring layer 10 is not particularly limited, for example, when the wiring layer 10 is formed from copper foil, the thickness of the wiring layer 10 is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. If the thickness is less than 5 μm, production stability and handling properties tend to decrease.

[0029] <Polyimide insulating layer> The polyimide insulating layer 100 in contact with the wiring layer 10, which constitutes the circuit board of the present invention, has the following characteristics (i) to (iv). When the circuit board has a plurality of polyimide insulating layers 100 in contact with the wiring layer 10, each polyimide insulating layer preferably has the following characteristics (i) to (iv).

[0030] (i) Coefficient of thermal expansion (CTE) The coefficient of thermal expansion (CTE) of the polyimide insulating layer 100 is in the range of 10 to 30 ppm / K. By setting the coefficient of thermal expansion of the polyimide insulating layer 100 in this range, it is possible to prevent warpage and a decrease in dimensional stability in the circuit board. The coefficient of thermal expansion of the polyimide insulating layer 100 is preferably 10 to 25 ppm / K, and more preferably in the range of 15 to 25 ppm / K. If the coefficient of thermal expansion is less than 10 ppm / K or more than 30 ppm / K, warpage may occur or dimensional stability may decrease.

[0031] The thermal expansion coefficient of the polyimide insulating layer 100 is determined by the thermal expansion coefficient and thickness of the non-thermoplastic polyimide layer 110, and the thermal expansion coefficient and thickness of the thermoplastic polyimide layers 120A and 120B. The non-thermoplastic polyimide layer 110 has lower thermal expansion properties than the thermoplastic polyimide layers 120A and 120B, and the coefficient of thermal expansion (CTE) of the non-thermoplastic polyimide layer 110 is preferably in the range of 1 to 25 ppm / K, more preferably in the range of 3 to 25 ppm / K. On the other hand, the thermal expansion coefficient of the thermoplastic polyimide layers 120A and 120B is preferably 35 ppm / K or more, more preferably 35 to 80 ppm / K, and even more preferably within the range of 35 to 70 ppm / K.

[0032] The thermal expansion coefficients of the thermoplastic polyimide layers 120A, 120B and the non-thermoplastic polyimide layer 110 can be adjusted to desired values ​​by appropriately changing the combination of raw materials forming the polyimide layers, the drying and curing conditions, and the thickness of the polyimide layers.

[0033] (ii) Oxygen permeability The oxygen permeability of the polyimide insulating layer 100 is 1.8×10 -12 mol / (m 2 This oxygen permeability can be measured in accordance with the differential pressure method (JIS K7126-1) by isolating the polyimide insulating layer from the circuit board, defining the area for oxygen permeability measurement with a specific slit, as will be described in the Examples.

[0034] Furthermore, when the circuit board has a plurality of polyimide insulating layers in contact with the wiring layer, this oxygen permeability is the oxygen permeability of each polyimide insulating layer.

[0035] The oxygen permeability of the polyimide insulating layer 100 is 1.8×10 -12 mol / (m 2 By controlling the oxygen permeability to 1.8×10 s Pa or less, the adhesion between the wiring layer 10 and the polyimide insulating layer 100 can be maintained well for a long period of time even when the circuit board is placed in an environment where it is repeatedly exposed to high temperatures. -12 mol / (m 2 If the pressure exceeds 100 kJ / cm 2 , when the circuit board is repeatedly exposed to high temperatures, oxygen that has permeated the polyimide insulating layer 100 will cause oxidation of the wiring layer 10, resulting in a decrease in adhesion between the wiring layer 10 and the polyimide insulating layer 100.

[0036] (iii) Proportion of monomer residues having a biphenyl skeleton In the polyimide insulating layer 100, the proportion of monomer residues having a biphenyl skeleton (hereinafter also referred to as biphenyl skeleton-containing residues) calculated by the following formula (1) relative to all monomer residues derived from all monomer components constituting the non-thermoplastic polyimide layer and thermoplastic polyimide layer constituting the polyimide insulating layer 100 is 50 mol % or more.

[0037]

number

[0038] In formula (1), n ​​is the total number of non-thermoplastic polyimide layers and thermoplastic polyimide layers constituting the polyimide insulating layer 100, and is an integer of 2 or more; M i is the proportion (unit: mol%) of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components in the polyimide constituting the i-th polyimide layer of the polyimide insulating layer 100, and L i is the thickness of the i-th polyimide layer, and L is the thickness of the polyimide insulating layer 100.

[0039] When the proportion of the biphenyl skeleton-containing monomer residues calculated by formula (1) is 50 mol% or more, the rigid structure derived from the monomer facilitates the formation of an ordered structure throughout the polymer, thereby reducing oxygen permeability and suppressing molecular motion, thereby reducing the dielectric loss tangent. In contrast, when the proportion of the biphenyl skeleton-containing residues is less than 50 mol%, the dielectric loss tangent is not sufficiently reduced. Furthermore, reducing the thickness of the polyimide insulating layer 100 does not sufficiently reduce the oxygen permeability. As a result, when used on, for example, a circuit board, the long-term heat-resistant adhesiveness becomes insufficient and the polyimide insulating layer 100 is not suitable for high-speed transmission. From this perspective, the proportion of the biphenyl skeleton-containing residues calculated by formula (1) is preferably 60 mol% or more, and more preferably 65 mol% or more. On the other hand, in order for the polyimide insulating layer 100 to maintain the physical properties required for a circuit board material, the proportion of the biphenyl skeleton-containing residues calculated by formula (1) is preferably 80 mol% or less.

[0040] Here, the biphenyl skeleton is a skeleton in which two phenyl groups are single-bonded, as shown in the following formula (a). Therefore, examples of monomer residues having a biphenyl skeleton include monomer residues having a biphenyldiyl group, a biphenyltetrayl group, etc. The aromatic rings contained in these residues may have any substituent.

[0041] Representative examples of biphenyldiyl groups include those represented by the following formula (b): Representative examples of biphenyltetrayl groups include those represented by the following formula (c): In the biphenyldiyl group and biphenyltetrayl group, the bonding positions on the aromatic ring are not limited to those shown in formula (b) and formula (c), and as described above, the aromatic rings contained in these residues may have any substituent.

[0042] [ka]

[0043] The monomer residue having a biphenyl skeleton has a structure derived from the raw material monomers of the non-thermoplastic polyimide layer and the thermoplastic polyimide layer that constitute the polyimide insulating layer 100, and may be derived from an acid dianhydride or a diamine compound.

[0044] Representative examples of acid dianhydride residues having a biphenyl skeleton include residues derived from acid dianhydrides such as 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride, and 4,4'-biphenol-bis(trimellitate anhydride). Among these, acid dianhydride residues derived from BPDA (hereinafter also referred to as "BPDA residues") are particularly preferred because they facilitate the formation of ordered polymer structures and reduce dielectric loss tangent and hygroscopicity by suppressing molecular motion. Furthermore, BPDA residues can impart self-supporting properties to gel films as polyamic acids of polyimide precursors.

[0045] Representative examples of diamine compounds having a biphenyl skeleton include diamine compounds having only two aromatic rings, such as 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-dipropoxy-4,4'-diaminobiphenyl (m-POB), 2,2'-di-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB). The residues derived from these diamine compounds have a rigid structure and therefore have the effect of imparting an ordered structure to the entire polymer. By containing residues derived from these diamine compounds, a polyimide having low oxygen permeability and low moisture absorption can be obtained, and the amount of moisture inside the molecular chain can be reduced, thereby lowering the dielectric loss tangent.

[0046] (iv) Imide group concentration of the non-thermoplastic polyimide layer The imide group concentration in the non-thermoplastic polyimide layer that constitutes the polyimide insulating layer 100 is 33% by weight or less. Here, "imide group concentration" refers to the molecular weight of the imide group (-(CO)2-N-) in the non-thermoplastic polyimide divided by the molecular weight of the entire non-thermoplastic polyimide structure. If the imide group concentration exceeds 33 wt%, the moisture absorption increases due to the increase in polar groups. On the other hand, decreasing the imide group concentration tends to increase the thermal expansion coefficient of the polyimide layer. However, by controlling the molecular orientation in the non-thermoplastic polyimide by selecting the appropriate combination of acid dianhydride and diamine compound, the increase in the thermal expansion coefficient associated with a decrease in the imide group concentration can be suppressed, ensuring low moisture absorption. Furthermore, in order to ensure adhesion between the electroless plating and the polyimide during electroless plating of the via holes, the imide group concentration in the non-thermoplastic polyimide layer constituting the polyimide insulating layer 100 is preferably 20% by weight or more, more preferably 25% by weight or more.

[0047] The imide group concentration in the thermoplastic polyimide layer constituting the polyimide insulating layer 100 is also preferably 30% by weight or less. Here, "imide group concentration" refers to the value obtained by dividing the molecular weight of the imide group (-(CO)2-N-) in the thermoplastic polyimide by the molecular weight of the entire thermoplastic polyimide structure. If the imide group concentration in the thermoplastic polyimide layer exceeds 30% by weight, the elastic modulus at temperatures above the glass transition temperature becomes difficult to decrease, and the increase in polar groups deteriorates the low moisture absorption properties. Furthermore, in order to ensure adhesion between the electroless plating and the polyimide during electroless plating of the via holes, the imide group concentration in the thermoplastic polyimide layer constituting the polyimide insulating layer 100 is preferably 20% by weight or more, more preferably 25% by weight or more.

[0048] In addition to the above characteristics (i) to (iv), the polyimide insulating layer 100 preferably further satisfies the following condition (v). (v) The proportion of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components in the thermoplastic polyimide layer is 30 mol % or more.

[0049] When the proportion of monomer residues having a biphenyl skeleton among all monomer residues constituting the thermoplastic polyimide layer is 30 mol % or more, an ordered structure is formed throughout the polymer due to the rigid structure derived from the monomer, resulting in a thermoplastic polyimide layer that is thermoplastic yet has low oxygen permeability and moisture absorption, excellent long-term heat-resistant adhesion, and a low dielectric loss tangent. As shown in Figure 2, when the circuit board has thermoplastic polyimide layers 120A and 120B on both sides of the non-thermoplastic polyimide layer 110, it is sufficient that either one of the thermoplastic polyimide layers 120A or 120B satisfies the above condition (v), but it is preferable that both the thermoplastic polyimide layers 120A and 120B satisfy the above condition (v).

[0050] <Thickness> The overall thickness T1 of the polyimide insulating layer 100 of this embodiment can be set within a predetermined range depending on the purpose of use, and is preferably within the range of 30 to 60 μm, and more preferably within the range of 35 to 50 μm. If the thickness T1 is less than the above lower limit, it becomes difficult to sufficiently reduce the oxygen permeability, and there is a concern that the adhesion between the wiring layer 10 and the polyimide insulating layer 100 may decrease when repeatedly exposed to high temperatures. On the other hand, if the thickness T1 exceeds the above upper limit, problems such as cracks occurring when the polyimide film is bent may occur, causing breakage.

[0051] Furthermore, the ratio T2 / T1 of the total thickness T2 of the thermoplastic polyimide layers 120A and 120B to the thickness T1 of the polyimide insulating layer 100 (here, T2 means T2A in FIG. 1 and T2A+T2B in FIG. 2) is preferably 0.17 or less, and more preferably in the range of 0.10 to 0.15. If this ratio is greater than 0.17, the oxygen permeability increases and it becomes difficult to reduce the dielectric tangent. Therefore, when used in, for example, a circuit board, the long-term heat-resistant adhesion becomes insufficient and it becomes difficult to apply to high-speed transmission.

[0052] The lower limit of the ratio T2 / T1 is not particularly limited. This is because the smaller the ratio T2 / T1, the easier it is to reduce the oxygen permeability and the dielectric loss tangent. However, since the smaller the ratio T2 / T1, the relatively smaller the thickness proportion of the thermoplastic polyimide layers 120A, 120B, the lower limit of the ratio T2 / T1 is preferably, for example, about 0.02, which is a value that ensures the adhesive reliability between the polyimide insulating layer 100 and the wiring layer 10.

[0053] Furthermore, the thickness T3 of the non-thermoplastic polyimide layer 110 can be set within a predetermined range depending on the purpose of use, and is preferably within the range of 25 to 49 μm, and more preferably within the range of 30 to 49 μm. If the thickness T3 is less than the above lower limit, the effect of improving the dielectric properties of the polyimide insulating layer 100 will be reduced, and the oxygen permeability will increase, which may result in a decrease in adhesion between the wiring layer 10 and the polyimide insulating layer 100 when repeatedly exposed to high temperatures.

[0054] <General synthesis method of polyimide> Generally, polyimides can be produced by reacting an acid dianhydride with a diamine compound in a solvent to form a polyamic acid, followed by heating to close the ring (imidization). For example, approximately equimolar amounts of the acid dianhydride and the diamine compound are dissolved in an organic solvent, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, thereby obtaining a polyamic acid, which is a precursor to polyimide. During the reaction, the reaction components are dissolved in the organic solvent so that the resulting precursor is in the range of 5 to 30 wt %, preferably 10 to 20 wt %, of the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such organic solvents used is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 30% by weight.

[0055] The synthesized polyamic acid is usually advantageously used as a solution in a reaction solvent, but it can be concentrated, diluted, or replaced with another organic solvent as necessary. Furthermore, polyamic acid is generally advantageously used because of its excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 cps to 100,000 cps. If the viscosity is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating using a coater or the like. The method for imidizing polyamic acid is not particularly limited, and a suitable method is, for example, heat treatment in the solvent at a temperature within the range of 80 to 400°C for 1 to 24 hours. Next, non-thermoplastic polyimides and thermoplastic polyimides will be described in more detail.

[0056] <Non-thermoplastic polyimide> The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 110 contains acid dianhydride residues and diamine residues. The non-thermoplastic polyimide preferably contains 60 mol % or more, and more preferably 70 mol % or more, of biphenyl skeleton-containing residues among all monomer residues derived from all monomer components. By making the biphenyl skeleton-containing residues in the non-thermoplastic polyimide 60 mol % or more, the content ratio of biphenyl skeleton-containing residues in the entire polyimide constituting the polyimide insulating layer 100 can be increased, thereby reducing oxygen permeability and achieving a low dielectric loss tangent.

[0057] (Acid dianhydride residue) The non-thermoplastic polyimide preferably contains 35 mol % or more, more preferably 50 mol % or more, of all acid dianhydride residues having a biphenyl skeleton, and even more preferably contains the above amount of biphenyltetrayl groups represented by formula (c).

[0058] In addition to the above-described acid dianhydride residue having a biphenyl skeleton, the non-thermoplastic polyimide may contain residues of acid dianhydrides commonly used as raw materials for polyimides, provided that the effects of the present invention are not impaired. Examples of such acid dianhydride residues include pyromellitic dianhydride (PMDA), 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 2,2',3,3'-, 2,3,3',4'-, or 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, and 4,4'-oxydiphthalic anhydride. -benzophenone tetracarboxylic dianhydride, 2,3',3,4'-diphenyl ether tetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyl tetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3.4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene-tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1 Examples of acid dianhydride residues include those derived from aromatic tetracarboxylic dianhydrides such as 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11-, or 5,6,11,12-perylene-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and ethylene glycol bisanhydrotrimellitate.

[0059] (diamine residue) The non-thermoplastic polyimide preferably contains 70 mol % or more, and more preferably 85 mol % or more, of all diamine residues having a biphenyl skeleton. It is even more preferable that the non-thermoplastic polyimide contains the biphenyldiyl group represented by formula (b) in the above-mentioned amount. The biphenyldiyl group represented by formula (b) has a rigid structure and acts to impart an ordered structure to the entire polymer, thereby reducing oxygen permeability and reducing the dielectric loss tangent by suppressing molecular motion.

[0060] In addition to the diamine residue having a biphenyl skeleton, the non-thermoplastic polyimide may contain residues of diamine compounds generally used as raw materials for polyimides, as long as the effects of the invention are not impaired. Examples of such diamine residues include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 4-aminophenyl-4'-aminobenzoate (APAB), 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, (3,3'-bisamino)diphenylamine, 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, 1,3-bis(4-aminophenoxy)benzylamine, 1,4-bis(3-aminophenoxy)benzylamine, 1,4-bis(4 ... nophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline, bis[4,4'-(3-aminophenoxy)]benzanilide, 4-[3-[4-( 4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane Pan, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl) )methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-d-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5 -Diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, 6-amino-2-(4-aminophenoxy)benzoxazole, 2,6-diamino-3,5-diethyltoluene, 2,4-diamino-3,Examples include diamine residues derived from aromatic diamine compounds such as 5-diethyltoluene, 2,4-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, and bis(4-amino-3-ethyl-5-methylphenyl)methane, and diamine residues derived from aliphatic diamine compounds such as dimer acid-type diamines in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.

[0061] In non-thermoplastic polyimides, the oxygen permeability, dielectric properties, thermal expansion coefficient, storage modulus, tensile modulus, etc. can be controlled by selecting the types of the acid dianhydride residues and diamine residues, or by selecting the respective molar ratios when two or more types of acid dianhydride residues or diamine residues are used. Furthermore, in non-thermoplastic polyimides, when a plurality of polyimide structural units are present, they may be present as blocks or randomly, but are preferably present randomly.

[0062] The non-thermoplastic polyimide preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic acid dianhydride and an aromatic diamine residue derived from an aromatic diamine. By making both the acid dianhydride residue and the diamine residue contained in the non-thermoplastic polyimide aromatic groups, the dimensional accuracy of the polyimide insulating layer 100 in a high-temperature environment can be improved.

[0063] The weight-average molecular weight of the non-thermoplastic polyimide is, for example, preferably in the range of 10,000 to 400,000, more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during coating.

[0064] <Thermoplastic polyimide> In the polyimide insulating layer 100, the thermoplastic polyimide constituting the thermoplastic polyimide layers 120A and 120B contains acid dianhydride residues and diamine residues. As per the above condition (v), the thermoplastic polyimide preferably contains 30 mol % or more, and more preferably 40 mol % or more, of biphenyl skeleton-containing residues among all monomer residues derived from all monomer components. By making the biphenyl skeleton-containing residues in the thermoplastic polyimide 30 mol % or more, the content ratio of biphenyl skeleton-containing residues in the entire polyimide constituting the polyimide insulating layer 100 can be increased, thereby reducing oxygen permeability and achieving a low dielectric loss tangent. On the other hand, since it is necessary to improve the flexibility of the polyimide molecular chain and impart thermoplasticity to ensure adhesion to a metal layer, the upper limit of the content of biphenyl skeleton-containing residues is preferably 65 mol %.

[0065] (Acid dianhydride residue) The thermoplastic polyimide preferably contains 60 mol % or more of acid dianhydride residues having a biphenyl skeleton among all acid dianhydride residues, and more preferably contains the biphenyltetrayl group represented by the above formula (c) in the above amount.

[0066] In addition to the above-described acid dianhydride residues having a biphenyl skeleton, the thermoplastic polyimide may contain acid dianhydride residues generally used as raw materials for polyimides, provided that the effects of the present invention are not impaired. Examples of such acid dianhydride residues include the acid dianhydride residues exemplified for non-thermoplastic polyimides.

[0067] (diamine residue) The thermoplastic polyimide preferably contains 1 mol% or more, and more preferably 5 mol% or more, of diamine residues having a biphenyl skeleton among all diamine residues. It is even more preferable that the biphenyldiyl group represented by the aforementioned formula (b) is contained in the above-mentioned amount. The biphenyldiyl group represented by formula (b) has a rigid structure and has the effect of imparting an ordered structure to the entire polymer, thereby suppressing molecular motion and reducing the dielectric loss tangent and moisture absorption. Furthermore, by using it as a raw material for thermoplastic polyimide, polyimide with low oxygen permeability and excellent long-term heat-resistant adhesiveness can be obtained.

[0068] In addition to the diamine residue having a biphenyl skeleton, the thermoplastic polyimide may contain residues of diamine compounds generally used as raw materials for polyimides, provided that the effects of the present invention are not impaired. Examples of such diamine residues include residues of diamine compounds exemplified for non-thermoplastic polyimides.

[0069] In the thermoplastic polyimide, the thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the types of the acid dianhydride residue and diamine residue, or by selecting the molar ratio of each when two or more types of acid dianhydride residues or diamine residues are used. Furthermore, when the thermoplastic polyimide has a plurality of polyimide structural units, they may be present as blocks or randomly, but are preferably present randomly.

[0070] The thermoplastic polyimide preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic acid dianhydride and an aromatic diamine residue derived from an aromatic diamine. By making both the acid dianhydride residue and the diamine residue contained in the thermoplastic polyimide aromatic groups, degradation of the polyimide in a high-temperature environment of the polyimide insulating layer 100 can be suppressed.

[0071] As mentioned above, the imide group concentration in the thermoplastic polyimide layers 120A and 120B is preferably 30% by weight or less. If the imide group concentration exceeds 30% by weight, the elastic modulus at temperatures equal to or higher than the glass transition temperature becomes difficult to decrease, and the increase in polar groups also deteriorates the low moisture absorption property.

[0072] The weight-average molecular weight of the thermoplastic polyimide is preferably in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during coating.

[0073] In the polyimide insulating layer 100, the thermoplastic polyimide layers 120A and 120B function as adhesive layers for the wiring layer 10 and can improve adhesion to a metal layer such as copper foil. Therefore, the thermoplastic polyimide layers 120A and 120B preferably have a glass transition temperature in the range of 200°C or higher and 350°C or lower, and more preferably in the range of 200°C or higher and 320°C or lower.

[0074] Furthermore, since the thermoplastic polyimide layers 120A and 120B serve as adhesive layers for the wiring layer 10, a completely imidized structure is most preferable in order to suppress copper diffusion. However, a portion of the polyimide may be in the form of an amic acid. The imidization rate can be determined by measuring the infrared absorption spectrum of the polyimide thin film by the single-reflection ATR method using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO Corporation) at 1015 cm -1 Based on the benzene ring absorber near 1780cm -1 It is calculated from the absorbance of the C=O stretching derived from the imide group.

[0075] <Polyimide film form> In the present invention, the polyimide insulating layer 100 is not particularly limited as long as it satisfies the above conditions, and may be a film (sheet) made of insulating resin, for example, an insulating resin film laminated on a substrate such as a metal foil such as copper foil, a glass plate, or a resin sheet such as a polyimide film, a polyamide film, or a polyester film.

[0076] <Dielectric loss tangent> To reduce dielectric loss during high-frequency signal transmission, the polyimide insulating layer 100 preferably has a dielectric dissipation factor of 0.004 or less at 10 GHz as measured using a split-post dielectric resonator (SPDR). To improve the transmission loss of a circuit board, controlling the dielectric dissipation factor of the polyimide insulating layer is particularly important. By maintaining the dielectric dissipation factor within the above range, the effect of reducing transmission loss is enhanced. Therefore, when the circuit board of the present invention is used as a circuit board for high-frequency applications, transmission loss can be efficiently reduced. If the dielectric dissipation factor at 10 GHz exceeds 0.004, problems such as increased electrical signal loss are likely to occur along the high-frequency signal transmission path. While there is no particular lower limit for the dielectric dissipation factor at 10 GHz, consideration must be given to controlling the physical properties of the polyimide insulating layer 100.

[0077] <Dielectric constant> In the present invention, in order to ensure impedance matching, the polyimide insulating layer 100 as a whole preferably has a relative dielectric constant of 4.0 or less at 10 GHz. If the relative dielectric constant at 10 GHz exceeds 4.0, this leads to an increase in dielectric loss, which is likely to cause inconveniences such as increased loss of electrical signals on the transmission path of high-frequency signals.

[0078] <Filler> In the present invention, the polyimide insulating layer 100 may contain inorganic fillers or organic fillers in the non-thermoplastic polyimide layer 110 or the thermoplastic polyimide layers 120A and 120B as needed. Specific examples include inorganic fillers such as silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride, and organic fillers such as fluorine-based polymer particles and liquid crystal polymer particles. These may be used alone or in combination of two or more. When an organic filler is contained, it is not considered to be part of all the monomer components constituting the non-thermoplastic polyimide layer 110 or the thermoplastic polyimide layers 120A and 120B.

[0079] <Circuit board manufacturing method> The circuit board of the present invention can be obtained by preparing a metal-clad laminate in which a polyimide insulating layer 100 and a metal layer are laminated together, and then processing the metal-clad laminate by a conventional method for wiring. The metal-clad laminate can be obtained by sputtering or plating the metal that constitutes the wiring layer 10 onto the polyimide insulating layer 100, or by laminating a metal foil by a method such as thermocompression bonding.

[0080] The metal-clad laminate may be produced by casting a coating liquid containing a polyamic acid, which is a precursor of polyimide, onto a metal foil such as copper foil, drying the coating to form a coating film, and then heat-treating the coating to imidize it and form a polyimide layer. The polyimide insulating layer 100 can be manufactured as follows.

[0081] [Method of manufacturing polyimide insulating layer] As preferred embodiments of the method for producing the polyimide insulating layer 100, the following [1] to [3] can be exemplified. [1] A method of producing a polyimide insulating layer 100 by repeatedly applying a polyamic acid solution to a supporting substrate and drying it, followed by imidization. [2] A method of producing a polyimide insulating layer 100 by repeatedly applying a polyamic acid solution to a supporting substrate and drying it, and then peeling off the polyamic acid gel film from the supporting substrate and imidizing it. [3] A method of producing a polyimide insulating layer 100 by multi-layer extrusion, in which a polyamic acid solution is simultaneously applied and dried in a laminated state, and then imidized (hereinafter referred to as multi-layer extrusion method).

[0082] The method [1] above may include, for example, the following steps 1a to 1c: (1a) applying a polyamic acid solution to a supporting substrate and drying it; (1b) forming a polyimide layer by heat-treating polyamic acid on a supporting substrate to imidize it; (1c) obtaining a polyimide insulating layer 100 by separating the supporting substrate and the polyimide layer; may include:

[0083] The method [2] above may include, for example, the following steps 2a to 2c: (2a) applying a polyamic acid solution to a supporting substrate and drying; (2b) separating the support substrate from the polyamic acid gel film; (2c) heat-treating the gel film of polyamic acid to imidize it, thereby obtaining a polyimide insulating layer 100; may include:

[0084] In the above-mentioned method [1] or [2], by repeating step 1a or step 2a multiple times, a polyamic acid laminate structure can be formed on the support substrate. The method for applying the polyamic acid solution to the support substrate is not particularly limited, and it can be applied using, for example, a coater such as a comma coater, a die coater, a knife coater, or a lip coater.

[0085] The above method [3] can be carried out in the same manner as the above method [1] or [2], except that in step 1a of the above method [1] or step 2a of the above method [2], a polyamic acid laminate structure is simultaneously applied by multilayer extrusion and dried.

[0086] It is preferable to complete the imidization of polyamic acid on the supporting substrate to form the polyimide insulating layer 100. Since the polyamic acid resin layer is imidized while fixed to the supporting substrate, the expansion and contraction changes of the polyimide layer during the imidization process can be suppressed, and the thickness and dimensional accuracy of the polyimide insulating layer 100 can be maintained. [Example]

[0087] The features of the present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[0088] [Viscosity measurement] The viscosity was measured at 25°C using an E-type viscometer (Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the viscosity was read when the viscosity stabilized 2 minutes after the start of measurement.

[0089] [Measurement of glass transition temperature (Tg)] A 5 mm wide polyimide film was measured using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA G2) with a chuck distance of 23 mm during measurement, at a heating rate of 4°C / min from 30°C to 400°C, and at a frequency of 11 Hz. The temperature at which the change in elastic modulus (tan δ) reached its maximum was defined as the glass transition temperature. The storage modulus at 30°C measured using DMA was 1.0 x 10 9 Pa or more, and the storage modulus at 350°C is 1.0 × 10 8 Those showing a storage modulus of less than 1.0 x 10 Pa are considered "thermoplastic" and have a storage modulus of 1.0 x 10 Pa at 30°C. 9 Pa or more, and the storage modulus at 350°C is 1.0 × 10 8Those showing a thermal expansion coefficient of 100 Pa or more were categorized as "non-thermoplastic."

[0090] [Measurement of coefficient of thermal expansion (CTE)] A 3 mm wide polyimide film was heated from 30°C to 260°C at a constant heating rate while applying a 5.0 g load using a thermomechanical analyzer (trade name: TMA / SS6100, manufactured by Hitachi High-Technologies Corporation) with a chuck distance of 15 mm during measurement. The film was then held at that temperature for 10 minutes and then cooled at a rate of 5°C / min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 250°C to 100°C.

[0091] [Moisture absorption rate measurement] Two polyimide film test pieces (width: 4 cm × length: 25 cm) were prepared and dried for 1 hour at 80°C. Immediately after drying, they were placed in a constant temperature and humidity chamber at 23°C / 50% RH and left to stand for at least 24 hours. The weight change before and after the drying was calculated using the following formula. Moisture absorption rate (weight %) = [(weight after moisture absorption - weight after drying) / weight after drying] × 100

[0092] [Measurement of relative permittivity and dielectric loss tangent] The dielectric constant and dielectric loss tangent of the polyimide film were measured at a frequency of 10 GHz using a vector network analyzer (Agilent, product name: E8363C) and a split post dielectric resonator (SPDR resonator). The material used for the measurement was left for 24 hours under the conditions of temperature: 24-26°C and humidity: 45-55%.

[0093] [Calculation of imide group concentration] The imide group concentration was determined by dividing the molecular weight of the imide group (-(CO)2-N-) by the molecular weight of the entire polyimide structure.

[0094] [Measurement of copper foil surface roughness] The surface roughness of the copper foil was measured in tapping mode over an area of ​​80 μm × 80 μm on the copper foil surface using an AFM (manufactured by Bruker AXS, product name: Dimension Icon type SPM) and a probe (manufactured by Bruker AXS, product name: TESPA (NCHV), tip curvature radius 10 nm, spring constant 42 N / m), and the ten-point average roughness (Rzjis) was calculated.

[0095] [Measurement of initial peel strength] The copper foil of a copper-clad laminate (copper foil / multilayer polyimide layer) prepared in the Examples described below was subjected to circuit processing at 10 mm intervals in the resin coating direction to a width of 1 mm, and then cut into a width of 8 cm and a length of 4 cm. Peel strength was measured using a Tensilon tester (manufactured by Toyo Seiki Seisaku-sho, Ltd., product name: Strograph VE-1D) by fixing the polyimide layer surface of the cut measurement sample to an aluminum plate with double-sided tape, and peeling the circuit-processed copper foil in a 180° direction at a rate of 50 mm / min until it had been peeled 10 mm from the polyimide layer, at which point the median strength was determined and recorded as the initial peel strength.

[0096] [Measurement of peel strength after heating] The copper foil of the copper-clad laminate (copper foil / multilayer polyimide layer) prepared in the examples described below was subjected to 1 mm-wide circuit processing at 10 mm intervals in the resin coating direction, and then cut into 8 cm wide × 4 cm long pieces. The cut samples were stored in a hot air oven (in air) set to 150 °C and removed after 1000 hours. Peel strength was measured using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, Ltd., product name: Strograph VE-1D). The polyimide layer surface of the removed measurement sample was fixed to an aluminum plate with double-sided tape, and the circuit-processed copper foil was peeled off in a 180° direction at a rate of 50 mm / min. The median strength measured when 10 mm of the copper foil was peeled off from the polyimide layer was determined and used as the post-heat peel strength.

[0097] [Oxygen permeability measurement] As described in the Examples below, two 2.5 mm x 30 mm pieces of polyimide film were cut from the polyimide film isolated after microstrip line formation, excluding the perforated areas. Next, two pieces of adhesive aluminum tape (Toyo Aluminum Kitchen Aluminum Tape 70) were cut to a size of 58 mmφ. As shown in Figure 8, two slits 202, each with a width L2 of 2.0 mm and a length L3 of 20 mm, were formed in each of the two aluminum tapes 200 cut to a size with a diameter L1 of 58 mmφ. As shown in Figure 9, two cut-out polyimide films 100x were bonded to the adhesive surface 201 of one of the aluminum tapes 200 with the slits 202 formed therein, covering the slits 202. Next, another aluminum tape 200 with the slits 202 formed therein was bonded to the surface bonded to the polyimide film 100x, with the slits 202 aligned with the other aluminum tape 200, to obtain an oxygen permeability measurement sample 100s.

[0098] The oxygen gas permeability of 100 samples obtained was measured according to the differential pressure method (gas volume measurement: gas chromatography) of JIS K7126-1 at a temperature of 23°C ± 2°C and a humidity of 65% ± 5%. The oxygen permeability measurement was performed using a GTR-30XA oxygen permeability measuring device manufactured by GTR Tech Co., Ltd. The differential pressure was 1 atm, and the polyimide film thickness (the sum of the first, second, and third layers) was as shown in Table 1. The amount of permeated oxygen was measured according to ISO 15105-1 using a G2700T·F manufactured by Yanaco Technical Science Co., Ltd. In this case, the effective area for measuring oxygen permeability was 0.8 cm , which is the effective permeation area of ​​the polyimide film. 2 It was calculated as:

[0099] [ 1 Composition analysis of each polyimide layer using H-NMR] After measuring the oxygen permeability, a portion of the polyimide film was cut out, washed with acetone, and dried. After drying, the first layer of the polyimide film was scraped off to the extent necessary for the measurement, and then decomposed in high-temperature alkaline methanol. Next, regarding this decomposition solution,1 The polyimide composition was analyzed by H-NMR (600 MHz). To confirm that the cut-out portion had not become the second layer, FT-IR measurements were also performed. It was confirmed that there was no change in the peaks in the cut-out portion.

[0100] Next, we will measure the third layer in the same way as we measured the first layer. 1 The polyimide composition was analyzed by H-NMR (600 MHz).

[0101] Finally, after confirming that the first layer has been completely removed using FT-IR, the second layer is removed and the measurement is performed in the same way as the first and third layers. 1 The polyimide composition was analyzed by H-NMR (600 MHz).

[0102] [Measurement of polyimide layer thickness] The copper foil of the copper-clad laminate described in the Examples below was etched away using an aqueous ferric chloride solution to obtain a polyimide film. The resulting polyimide film was cut into strips, embedded in resin, and then cut in the thickness direction with a microtome to prepare ultrathin sections of approximately 100 nm. The prepared ultrathin sections were observed using the STEM function of a Hitachi High-Tech SEM (SU9000) at an accelerating voltage of 30 kV. The thickness of each polyimide layer was measured at five points, and the average value was used as the thickness of each polyimide layer.

[0103] The abbreviations used in the Examples and Reference Examples represent the following compounds. PMDA: Pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene TPE-Q: 1,4-bis(4-aminophenoxy)benzene DAPE: 4,4'-diamino-diphenyl ether PDA: Paraphenylenediamine BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane Bisaniline-P: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Fine Chemicals, Inc., trade name: Bisaniline-P) DDA: aliphatic diamine having 36 carbon atoms (manufactured by Croda Japan, trade name: PRIAMINE 1074, amine value: 210 mg KOH / g, mixture of dimer diamines with cyclic and chain structures, dimer content: 95% by weight or more) DMAc: N,N-dimethylacetamide

[0104] (Synthesis Example 1) Under a nitrogen stream, 12.061 g of m-TB (0.0568 mol), 0.923 g of TPE-Q (0.0032 mol), and 1.0874 g of bisaniline-P (0.0032 mol) were added to a 300 ml separable flask, and DMAc was added in an amount to give a solids concentration of 15 wt% after polymerization. The mixture was stirred at room temperature to dissolve. Next, 6.781 g of PMDA (0.0311 mol) and 9.147 g of BPDA (0.0311 mol) were added, and the mixture was stirred at room temperature for 3 hours to carry out the polymerization reaction, yielding polyamic acid solution A. The solution viscosity of polyamic acid solution A was 29,800 cps.

[0105] Next, polyamic acid solution a was uniformly applied to copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rzjis on the resin side: 2.1 μm) to a thickness of approximately 25 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, a stepwise heat treatment from 120°C to 360°C was performed within 30 minutes to complete the imidization. The copper foil of the resulting copper-clad laminate was etched away using an aqueous ferric chloride solution to prepare polyimide film a (non-thermoplastic, Tg: 316°C, moisture absorption: 0.61 wt%). The imide group concentration of the polyimide constituting polyimide film a was 31.6 wt%.

[0106] (Synthesis Example 2) Under a nitrogen stream, 11.825 g of m-TB (0.0557 mol), 0.905 g of TPE-Q (0.0031 mol), 1.653 g of DDA (0.0031 mol), and an amount of DMAc such that the solids concentration after polymerization was 15 wt% were added to a 300 ml separable flask and stirred at room temperature to dissolve. Next, 6.649 g of PMDA (0.0305 mol) and 8.968 g of BPDA (0.0305 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution b. The solution viscosity of polyamic acid solution b was 27,800 cps.

[0107] Next, polyamic acid solution b was uniformly applied to copper foil 1 to a cured thickness of approximately 25 μm, and then heated and dried at 120°C to remove the solvent. Further, a stepwise heat treatment from 120°C to 360°C was performed within 30 minutes to complete the imidization. The copper foil of the resulting copper-clad laminate was etched away using an aqueous ferric chloride solution to prepare polyimide film b (non-thermoplastic, Tg: 258°C, moisture absorption rate: 0.54 wt%). The imide group concentration of the polyimide constituting polyimide film b was 30.9 wt%.

[0108] (Synthesis Example 3) Under a nitrogen stream, 11.920 g of m-TB (0.0562 mol) and 2.897 g of TPE-Q (0.0099 mol) were added to a 300 ml separable flask, along with DMAc in an amount to give a solids concentration of 15 wt% after polymerization, and the mixture was stirred at room temperature to dissolve. Next, 11.354 g of PMDA (0.0521 mol) and 3.829 g of BPDA (0.0130 mol) were added, followed by stirring at room temperature for 3 hours to carry out the polymerization reaction, yielding polyamic acid solution c. The solution viscosity of polyamic acid solution c was 31,200 cps.

[0109] Next, polyamic acid solution c was uniformly applied to copper foil 1 to a thickness of approximately 25 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, a stepwise heat treatment from 120°C to 360°C was performed within 30 minutes to complete the imidization. The copper foil was then etched away from the resulting copper-clad laminate using an aqueous ferric chloride solution to prepare polyimide film c (non-thermoplastic, Tg: 375°C, moisture absorption rate: 0.81 wt%). The imide group concentration of the polyimide constituting polyimide film c was 33.2 wt%.

[0110] (Synthesis Example 4) Under a nitrogen stream, 1.548 g of PDA (0.0143 mol) and 11.465 g of DAPE (0.0573 mol) were added to a 300 ml separable flask, along with DMAc in an amount to give a solids concentration of 15 wt% after polymerization, and the mixture was stirred at room temperature to dissolve. Next, 10.764 g of PMDA (0.0494 mol) and 6.223 g of BPDA (0.0212 mol) were added, and the mixture was stirred at room temperature for 3 hours to polymerize the mixture, yielding polyamic acid solution d. The solution viscosity of polyamic acid solution d was 23,500 cps.

[0111] Next, polyamic acid solution d was cast through a slit in a T-die mold to a thickness of 25 μm after curing, extruded onto a smooth belt-shaped metal support in a drying oven to form a thin film, heated at 130°C for a predetermined time, and then peeled off from the support to obtain a self-supporting film. This self-supporting film was then held at both ends in the width direction and inserted into a continuous heating oven. The film was heated from 100°C to a maximum temperature of 380°C, and imidized to prepare polyimide film d (non-thermoplastic, Tg >400°C, moisture absorption rate 1.14 wt%). The imide group concentration of the polyimide constituting polyimide film d was 36.2 wt%.

[0112] (Synthesis Example 5) Under a nitrogen stream, 15.591 g of BAPP (0.0380 mol) and an amount of DMAc sufficient to give a solids concentration of 12 wt% after polymerization were added to a 300 ml separable flask and stirred at room temperature to dissolve. Next, 8.409 g of PMDA (0.0386 mol) was added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution e. The solution viscosity of polyamic acid solution e was 2,350 cps.

[0113] Next, polyamic acid solution e was uniformly applied to copper foil 1 to a thickness of approximately 10 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, a stepwise heat treatment from 120°C to 360°C was performed within 30 minutes to complete the imidization. The copper foil of the resulting copper-clad laminate was etched away using an aqueous ferric chloride solution to prepare polyimide film e (thermoplastic, Tg: 320°C, moisture absorption rate: 0.55 wt%). The imide group concentration of the polyimide constituting polyimide film e was 23.6 wt%.

[0114] (Synthesis Example 6) Under a nitrogen stream, 1.847 g of m-TB (0.0087 mol) and 10.172 g of TPE-R (0.0348 mol) were added to a 300 ml separable flask, along with DMAc in an amount to give a solids concentration of 12 wt% after polymerization, and the mixture was stirred at room temperature to dissolve. Next, 2.889 g of PMDA (0.0132 mol) and 9.092 g of BPDA (0.0309 mol) were added, followed by stirring at room temperature for 3 hours to allow the polymerization reaction to proceed, yielding polyamic acid solution f. The solution viscosity of polyamic acid solution f was 2,210 cps.

[0115] Next, polyamic acid solution f was uniformly applied to copper foil 1 to a thickness of approximately 10 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, a stepwise heat treatment from 120°C to 360°C was performed within 30 minutes to complete the imidization. The copper foil of the resulting copper-clad laminate was etched away using an aqueous ferric chloride solution to prepare polyimide film f (thermoplastic, Tg: 226°C, moisture absorption rate: 0.41 wt%). The imide group concentration of the polyimide constituting polyimide film f was 27.4 wt%.

[0116] [Example 1] Polyamic acid solution f was uniformly applied to copper foil 2 (electrolytic copper foil, thickness: 12 μm, surface roughness Rzjis on the resin side: 0.6 μm) to a thickness of 2.5 μm after curing, and then heated and dried at 120°C for 1 minute to remove the solvent. Polyamic acid solution a was then uniformly applied to the resulting thickness of 25 μm after curing, and then heated and dried at 120°C for 3 minutes to remove the solvent. Polyamic acid f was then uniformly applied to the resulting thickness of 2.5 μm after curing, and then heated and dried at 120°C for 1 minute to remove the solvent. Subsequently, a stepwise heat treatment was performed from 140°C to 360°C to complete the imidization, and a single-sided copper-clad laminate 1 was prepared.

[0117] The initial peel strength and post-heat peel strength of the obtained single-sided copper-clad laminate 1 were measured and found to be 1.06 kN / m and 0.69 kN / m, respectively. The measurement results are shown in Table 1.

[0118] The copper foil of the single-sided copper-clad laminate 1 was etched away using an aqueous ferric chloride solution to obtain polyimide film 1a. The CTE and dielectric properties of the obtained polyimide film 1a were evaluated, revealing a CTE of 22 ppm / K, a dielectric constant of 3.56, and a dissipation factor of 0.0032. The measurement results are shown in Table 2.

[0119] The prepared single-sided copper-clad laminate 1 was then cut to a 20 cm x 20 cm size. The polyimide surface was then laminated to the roughened surface of copper foil 2 (electrolytic copper foil, thickness: 12 μm, surface roughness Rzjis on the resin side: 0.6 μm) cut to the same size, and the laminate was pressed at 330 °C for 10 minutes under a pressure of 6.5 MPa to prepare a double-sided copper-clad laminate 2. After drilling holes to connect the ground layer to the prepared double-sided circuit laminate 2, through-hole connections were made and 10 μm of electrolytic copper plating was performed on the copper foil 2. Next, multiple circuits were formed on the double-sided copper-clad laminate 2, with signal wiring measuring 60 μm wide and 50 mm long formed on the copper layer on one surface and the other copper layer acting as the ground layer. A coverlay film (SAFY) manufactured by Nikkan Industries was then pressed onto the formed wiring surface at 160 °C for 90 minutes under a pressure of 4 MPa to prepare multiple microstrip lines.

[0120] Next, one piece of the prepared microstrip line was cut and immersed in N-methylpyrrolidone for 24 hours to peel off the coverlay film. After 24 hours, the swollen coverlay film was peeled off to isolate the circuit board with the signal wiring formed thereon, and then the circuit board with the signal wiring formed thereon was immersed in an aqueous ferric chloride solution to isolate a partially perforated polyimide film 1a'. The perforated portion was then removed to obtain a 5 mm x 40 mm polyimide film 1a'. The obtained polyimide film 1a' was subjected to oxygen permeability measurement and 1 The composition of the polyimide in each layer was analyzed using H-NMR. The oxygen permeability measurement results are shown in Table 3. Note that the composition analysis of the polyimide was omitted because the feed ratio was the same as that described in the synthesis example.

[0121] [Examples 2 to 4, Comparative Example 1, and Reference Examples 1 and 2] Single-sided copper-clad laminates 2-4, single-sided copper-clad laminate 5, single-sided copper-clad laminates 6-7, polyimide films 2a-4a, polyimide film 5a, and polyimide films 6a-7a of Examples 2-4, Comparative Example 1, and Reference Examples 1-2 were obtained in the same manner as in Example 1, except that the polyamic acid solutions shown in Table 1 were used and the thickness configurations were changed. The measurement results are shown in Tables 1 and 2.

[0122] Furthermore, for the obtained single-sided copper-clad laminates, preparation of double-sided copper-clad laminates, formation of microstrip lines, and isolation of the polyimide film after microstrip line formation were carried out in the same manner as in Example 1, except that the press temperature for copper foil compression bonding during preparation of the double-sided copper-clad laminates of Example 4 and Comparative Example 1 was changed to 380°C, thereby obtaining polyimide films 2a' to 4a', polyimide film 5a', and polyimide films 6a' to 7a'. The oxygen permeability of the obtained polyimide films was measured, and the results are shown in Table 3. Regarding the composition analysis of the polyimides, the feed ratio was the same as that described in the synthesis examples, as in Example 1, so description is omitted.

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] Comparative Example 2 Polyamic acid solution d was cast through a slit in a T-die mold to a thickness of 30 μm after curing, extruded onto a smooth, belt-shaped metal support in a drying oven to form a thin film, heated at 130°C for a predetermined time, and then peeled off from the support to obtain a self-supporting film. Furthermore, while the self-supporting film was continuously conveyed, polyamic acid solution e was applied to the air side of the self-supporting film using a die coater to a thickness of 2.5 μm after curing, and dried in a drying oven at 120°C for a predetermined time. Next, polyamic acid solution e was applied to the side opposite the coated side in the same manner as above to a thickness of 2.5 μm after curing, and dried in a drying oven at 120°C for a predetermined time.

[0127] The self-supporting film was held at both ends in the width direction and inserted into a continuous heating furnace, where it was heated from 100°C to a maximum heating temperature of 380°C, and imidized to obtain polyimide film 8b. Copper foil was placed on one side of this polyimide film 8b, and Teflon (registered trademark) film was placed on the other side. The film was then heated at a temperature of 320°C and a pressure of 340 MPa / m. 2 After the bonding, the Teflon (registered trademark) film was peeled off, thereby preparing a copper-clad laminate 8. The initial peel strength and post-heat peel strength of the obtained copper-clad laminate 8 were measured and found to be 1.15 kN / m and 1.01 kN / m, respectively.

[0128] The copper foil was removed from the single-sided copper-clad laminate 8 by etching in the same manner as in Example 1 to obtain a polyimide film 8a. The CTE and dielectric properties of the obtained polyimide film 8a were evaluated, and the results were CTE: 22 ppm / K, relative dielectric constant: 3.65, and dielectric dissipation factor: 0.0073.

[0129] Further, the preparation of a double-sided copper-clad laminate, the formation of a microstrip line, and the isolation of the polyimide film after the formation of the microstrip line were carried out in the same manner as in Example 1, except that the press temperature when the obtained single-sided copper-clad laminate 8 and the copper foil 2 were pressure-bonded was 380°C, thereby obtaining a polyimide film 8a'. The oxygen permeability of the obtained polyimide film 8a' was measured, and it was found to be 0.39 × 10 -12 [mol / (m 2 ·s·Pa)]. As for the composition analysis of the polyimide, the feed ratio was the same as that described in the synthesis example, as in Example 1, and therefore the description is omitted.

[0130] [Confirmation of via processing] Via holes with a diameter of 100 μm were formed in the double-sided copper-clad laminate 2 prepared in Example 1 using a laser via processing machine 1 (UV-YAG laser, manufactured by ESI, model number: ESI5335). After the via holes were formed, the cross sections were polished using a cross-section polisher and the cross sections were observed using a scanning electron microscope (SEM). No steps were observed between the polyimide layers, and the processability was good. An SEM photograph is shown in Figure 10. The arrows in Figure 10 indicate the copper foil.

[0131] In addition, a via hole with a diameter of φ150 μm was formed by a conformal method using a laser via processing machine 2 (CO laser, manufactured by Via Mechanics, model number: LC-2K212 / 2C) in the double-sided copper-clad laminate 2. After the via hole was formed, the cross section was polished using a cross-section polisher and observed under an SEM, confirming that the processability was good.

[0132] For the single-sided copper-clad laminate 3 prepared in Example 3, a double-sided copper-clad laminate was prepared in the same manner as in Example 1, and a through-hole of φ150 μm was formed using an NC drilling machine manufactured by Via Mechanics. After the through-hole was formed, the cross-section was polished using a cross-section polisher and observed under an SEM. No steps were observed between the polyimide layers, and the processability was good. An SEM photograph is shown in Figure 11. The arrow in Figure 11 indicates the copper foil.

[0133] [Confirmation of plating processability] After via holes were formed using a laser processing machine 1, the blind vias in the double-sided copper-clad laminate 2 were desmeared, followed by pre-plating and electroless plating. The cross section was polished using a cross-section polisher and observed under an SEM. No peeling of the polyimide layer or plating layer was observed, and plating processability was good. The SEM photograph is shown in Figure 12.

[0134] Furthermore, after through-holes were formed in the double-sided copper-clad laminate using an NC drilling machine, pre-plating and electroless plating were performed on the through-holes. The cross-sections were polished using a cross-section polisher and observed under an SEM. No peeling of the polyimide layer or plating layer was observed, and plating processability was good. The SEM photograph is shown in Figure 13.

[0135] Although the embodiments of the present invention have been described in detail above for the purpose of illustration, the present invention is not limited to the above-described embodiments and various modifications are possible. [Explanation of symbols]

[0136] 1A, 1B, 1C, 1D, 1E, 1F, 1G circuit boards 10 wiring layers 11 Signal line 12, 12', 12" ground layer 13 Shielded wiring 20 Adhesive layer 30 Coverlay 40 Via connection 100, 100', 100", 100A, 100B Polyimide insulating layer 100s Oxygen permeability measurement sample 110 Non-thermoplastic polyimide layer 120A, 120B Thermoplastic polyimide layers 130 Polyimide film 200 Aluminum Tape 201 Adhesive surface 202 Slit

Claims

1. A circuit board comprising a wiring layer and at least one polyimide insulating layer in contact with the wiring layer, and having a plurality of via connections, At least one of the via connections is formed in the polyimide insulating layer, and the polyimide insulating layer has a thermoplastic polyimide layer that is in direct contact with the wiring layer and a non-thermoplastic polyimide layer that is in indirect contact with the wiring layer; The polyimide insulating layer satisfies the following conditions (i) to (iv): (i) a thermal expansion coefficient in the range of 10 to 30 ppm / K; (ii) oxygen permeability of 1.8 × 10 -12 mol / (m 2 s·Pa) or less; (iii) the proportion of monomer residues having a biphenyl skeleton, calculated by the following formula (1), relative to all monomer residues derived from all monomer components constituting the non-thermoplastic polyimide layer and the thermoplastic polyimide layer is 50 mol % or more; (iv) the imide group concentration of the non-thermoplastic polyimide layer is 33% by weight or less; A circuit board characterized by satisfying the above. [Equation 1] [In formula (1), n ​​is the total number of non-thermoplastic polyimide layers and thermoplastic polyimide layers constituting the polyimide insulating layer, and is an integer of 2 or more; M ｉ is the proportion (unit: mol%) of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components in the polyimide constituting the i-th polyimide layer of the polyimide insulating layer, and L ｉ is the thickness of the i-th polyimide layer, and L is the thickness of the polyimide insulating layer.

2. 2. The circuit board according to claim 1, wherein the imide group concentration of the thermoplastic polyimide layer is 30% by weight or less.

3. In addition to the above conditions (i) to (iv), the following condition (v) is also met: (v) the proportion of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components in the thermoplastic polyimide layer is 30 mol % or more; 2. The circuit board according to claim 1, wherein the above formula (1) is satisfied.

4. 4. The circuit board according to claim 1, wherein the thickness of the polyimide insulating layer is within a range of 30 to 60 μm.

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